Weird tool .. Any ideas?

[Mud Hut]

Posting this item for a friend. It is an unusual iron tool, that measures right at 12" long and is 6 1/2 inches across the wishbone/roller section.
He says, " The end has a roller type part which seems to be stone but it sticks to a magnet. Even shavings of the "stone" that fell off while brushing it stick to a magnet."

I am stumped!

 

[OWK]

If I have to guess, I'd say it looks like a replaceable tool on an old uni-mat type machine that performs different functions.

This one looks like a sander or grinder. (maybe a blade sharpener)

Looks like it mounts to the machine by the foot, and a band drives the pulley on the end of your cylinder.

Does the cylinder seem to be made of abrasive material?

 

[nhbenz]

Pretty similar to part of a sickle blade sharpener, but I can't find a match.